There are a large number of malodorous molecules having different polarities and molecular weights in our living environment. Hitherto, a variety of methods have been developed for reducing various malodorous molecules. In general, the methods for reducing malodors are roughly classified into biological methods, chemical methods, physical methods, and sensory methods. Among malodorous molecules, short-chain fatty acids and amines having high polarities can be reduced by chemical methods, i.e., neutralization. Sulfur compounds such as thiol can be reduced by physical methods, i.e., absorptive treatment. However, there are still many malodorous molecules which cannot be reduced by known malodor reducing methods.
In addition, the known malodor reducing methods by the chemical neutralization or the absorptive treatment take long time for reducing the amounts of malodorous substances and thereby lack immediate effect. A method of reducing malodor by using an aromatic and thereby providing strong perception of another odor is also known. However, the odor of the aromatic may cause discomfort in this method. Moreover, these known methods may get rid of odors other than the target malodors. Thus, there is a demand for a malodor reducing method which can overcome these problems.
In mammals including humans, the mechanism for odorant recognition includes binding odorant molecules to olfactory receptors present on olfactory sensory neurons included in the olfactory epithelium, which is present in an upper portion of the nasal cavity, and transmitting the response of the receptors to the central nervous system. It has been reported that, 387 different olfactory receptors are present in human, and the genes encoding these olfactory receptors account for about 3% of the human genome. In general, a plurality of olfactory receptors responds to a plurality of odorant molecules. Specifically, one single olfactory receptor responds to a plurality of structurally similar odorant molecules at different affinities, while one single odorant molecule is detected by a plurality of olfactory receptors. It is also reported that a certain odorant molecule which can activate one olfactory receptor serves as an antagonist which inhibits activation of another olfactory receptor. Such combined response of these olfactory receptors leads to recognition of each odor.
Thus, when a first odorant molecule is co-present with a second odorant molecule, in some cases, the response of an olfactory receptor to the first odorant molecule is inhibited by the second odorant molecule. Through the inhibition, the odor of the first odorant molecule recognized by olfactory receptors may vary considerably. This mechanism is called “olfactory receptor antagonism.” Odor modulation by olfactory receptor antagonism can inhibits recognition specific to a malodor, and therefore differs in mechanism from a malodor reducing method by adding a perfume, an aromatic, or a like substance to the target odorant. In addition, the odor of an aromatic causing an unpleasant sensation to users can be prevented. Therefore, odor modulation based on olfactory receptor antagonism is a preferred means for reducing malodor.
In order to mask a malodor with an odor of, for example, a perfume or an aromatic, it is necessary to identify an odor substance exhibiting an effective malodor reducing function on the target malodorous substance. Hitherto, odors have been evaluated through a sensory test by specialists. However, the sensory test has problems. The problems include for example, odor-evaluators must be trained, and the throughput of the test is low. Thus, identification of an odor substance exhibiting a malodor reducing function is not easy.
A skin tanning agent (also called a self-tanning agent or a sunless tanning agent) is a skin cosmetic for staining the skin. As a component for providing skin with a brown color, dihydroxyacetone (DHA) is mainly used alone or together with, for example, erythrulose. These components react with the upper layer of the skin to change the color of skin to brown. This staining probably progresses by a browning reaction, but the details of the reaction mechanism have been hardly clarified. The browning reaction is also called a Maillard reaction in the food chemistry field and is a term referring to a reaction for generating a brown polymer called melanoidin by polymerizing a nitrogen-containing compound, such as an amino acid or a protein, and a reducing sugar. The Maillard reaction is caused by, for example, heating of a food and is involved in coloring of the food and generation of a flavor component.
Pyrazines are known to be generated by the Maillard reaction and as a component of a roasted aroma of a food. Patent Document 1 describes an odor-blocking agent including a functional pyrazine compound as an active ingredient for blocking the odor of an alkylpyrazine compound. Pyrazines are usually used as flavoring agents for flavoring foods, and the odors of pyrazines are rather utilized. In the food field, odors obtained by the Maillard reaction are reported in Non-Patent Document 1. In Non-Patent Document 1, the pyrazine compound is described as a preferred odor which characterizes a food. For example, 2,6-dimethylpyrazine is described as having a “sweet, fried, resembling fried potatoes, nutty, roasted” odor.